It is expensive to provide analog broadcast TV over a passive-optical network (PON) because of the high carrier-to-noise ratio (CNR) required of these signals(.about.50 dB/4 MHz). To achieve this high CNR performance, very linear transmitters must be used, and the transmission power level should be such to ensure that enough signal power (i.e. 0.2 mW) reaches the optical receiver. Since the output power of transmitters is limited, a single transmitter can only serve a limited number of receivers (unless expensive optical amplifiers are used). Because the optical receiver is not shared by many users in a fiber-to-the-home (FTTH) or fiber-to-the-curb (FTTC) systems, the cost of the transmitter will not be shared among many users. It therefore is quite expensive to provide broadcast analog video over a PON.
This problem is present in both wavelength-division-multiplexed PONs (where the light's wavelength determines which ONU receives the signal) and power-splitting PONs (where the light is split at a power-splitter, and all the ONU's receive the same signals).
One illustrative switched digital video system which broadcasts analog video signals is described in the article entitled "Video Services Delivery in Fiber in the Loop Systems Using MPEG Encoding and ATM Transport" by J. R. Jones, published in IEEE Lasers and Electro-Optics Society 1993 Annual Meeting, Nov. 15-18, 1993. This system is basically a hybrid-fiber-coax (HFC) system combined with a FTTC-PON. The broadcast signal is sent to a fiber-node, which then transmits the broadcast signals over coaxial cable serving many users (hundreds). The PON provides switched services to each ONU. The coaxial cable provides the ONU with power, and from the ONU the switched signals and the broadcast signals are transmitted to the home.
Undesirably, the prior art has not fully integrated the two systems (HFC and PON). Transmitting the broadcast signals to the neighborhood over a PON should lower the cost of deployment, operations and maintenance.